Transportable gas to liquid plant

ABSTRACT

A transportable GTL processing facility constructed on an inland barge is provided. Also provided is a process for producing liquid hydrocarbons from natural gas utilizing a transportable GTL processing facility. The facility and process may be used to access and convert stranded natural gas in an economical fashion into liquid hydrocarbons. Further provided is a transportable GTL processing facility and process for producing liquid hydrocarbons wherein the liquid hydrocarbons are upgraded into transportation fuels and other locally usable materials.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Application Ser. No.60/557,638, filed on Mar. 30, 2004.

FEDERALLY SPONSORED RESEARCH

Not applicable

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

FIELD OF THE INVENTION

This invention relates to gas-to-liquid (GTL) technology, and moreparticularly to GTL processes practiced on a mobile or transportableplatform. The invention further relates to a transportable GTL facilitywhich is capable of accessing stranded gas reserves.

BACKGROUND

Of the estimated 5,500 TCF of natural gas reserves worldwide, nearlyone-half is stranded, with over 50% of those reserves being offshore.For our purpose, the term “stranded gas” means natural gas that cannotbe economically delivered to market using current gas transportationmethods or current commercial GTL processes. Stranded gas includesassociated and flared/vented gas, and gas that is re-injected purely forregulatory compliance rather than for reservoir-pressure maintenance.Some of the factors that determine when a pipeline is profitable includeresource volume, transport route, pipeline distance, regulatoryenvironment, market size and demand growth. Excess reserves may beconsidered stranded where a paltry delivery rate is required to avoidoversupply of local markets. Negative economics may also arise fromtechnical complexity or expense associated with recovering and/orgathering the gas.

One method of producing stranded gas is to process it through aFischer-Tropsch (FT) gas-to-liquid (GTL) system. GTL is an applicationof the basic Fischer-Tropsch (FT) process, wherein synthesis gas (orsyngas, which is composed primarily of H₂ and CO) is reacted in thepresence of a Fischer-Tropsch catalyst to produce heavier hydrocarbons.Possible Fischer-Tropsch end products include kerosene, naphtha, waxes,liquid paraffins and lubes, synthetic diesel, gasoline, and jet fuel.Stranded natural gas may be used as a raw feedstock for GTL operations,thereby monetizing otherwise worthless gas.

SUMMARY OF THE INVENTION

The GTL barge provided by the invention is designed to develop naturalgas assets in the 0.5-5.0 TCF range where there is currently noinfrastructure to produce and transport the stranded reserves since thefields are not large enough to economically support an LNG facility. Byemploying the barge, the owner/operator of the field gets the addedbenefit of being able to book the reserves. The GTL barge includes asyngas generating section and a Fischer-Tropsch (FT) reaction section.The GTL barge is an inland barge and, therefore, not ocean-going. TheGTL barge is designed to be transportable to or near a gas formation bylift ship or other dry haul method. Product upgrading may also beincluded in the GTL barge, either integrated on the GTL inland barge orlocated near the GTL barge, such as on a separate barge or on-shore.

DETAILED DESCRIPTION OF THE INVENTION

The transportable GTL inland barge enables an exploration and productioncompany to produce and thus monetize stranded gas fields. The GTL bargefocuses on gas reserves in or near shallow water or onshore gas reservesthat are near the coastline or other navigable waterway.

The GTL barge is ideally suited to process associated rich gas thatmight otherwise be flared or re-injected. Estimated worldwide flared gasis about 10 billion ft³ per day. A single GTL barge, for example, may bedesigned to produce approximately 20,000 barrels per day (bpd) of totalliquid products, including approximately 12,000 bpd of GTL products.Assuming the natural gas has about 2 gpm propane and higher carbonnumber natural gas liquid (“NGL”); the combined NGL and GTL products areabout 8700 bpd of clean diesel fuel, 7300 bpd of naphtha, and 4400 bpdof LPG. The mobility and/or transportability of a GTL plant enables theoperator to mitigate long-term project and financial risk by having theability to relocate the barge. The GTL barges may be constructed inshipyards.

The GTL barge is used where it is within a distance from a gas reserveto-which it would be economically feasible to build a pipeline totransport natural gas feed to the barge. The products from the barge maybe either synthetic crude or upgraded products, including for example,transportation fuels.

Where there are two or more reserves located fairly close to each other,the reserves may be accumulated by pipeline or by compressed natural gas(“CNG”) to supply feedstock to a single GTL barge. Where two or snorebarges are located in a region, a single syncrude upgrading section mayserve such barges and the upgrading section may be located on one of thebarges, a separate barge or a separate location. A shuttle barge may beused to carry syncrude to the product upgrading unit.

In one embodiment of the invention, the GTL barge is constructed on aninland barge. As defined herein, the term “inland barge” means a bargewhich is transportable by lift ship or other form of barge dry haul andwhich is not suitable for towing or operation at sea or in any watershaving wave action greater than that of Sea State 0 (as defined byPierson—Moskowitz Sea Spectrum). It should be noted that the Sea State 0is based upon wind speeds of around three (3) knots. However, as usedherein, the term inland barge will include designs which may withstandwind loads of about 120 kilometers per hour or greater. The inlandbarge, however, may be towed within inland waters, such as rivers, lakesand intercoastal waterways. The inland barge is installed and thenoperated only in calm water. “Installed” is defined as either freelyfloating in confining moorings or fixed in a non-floating arrangement.Confining moorings will allow the barge to float on a water bodyallowing only uniform vertical motion with essentially no lateral ortwisting motion. In some embodiments, a barge having jacking legs may beused and installation of the jacking legs installs the barge. As usedherein, the term “calm water” means near shore, such as on pylons,beached, or in a natural or man-made inlet which may or may not bedammed and/or drained, or on a fixed platform if off-shore. The term“calm water” may also include inland waterways, such as rivers, lakes,ship channels, bayous, and intercoastal waterways which are protectedfrom substantial natural wave action. Other methods of securing thebarge in calm water include use of a flotation jacket surrounding theouter perimeter of the barge, anchoring, or installation of legs underthe barge. As used herein, the terms “GTL barge” and “GTL inland barge”are synonymous.

As the term is defined herein, inland barges are not intended foroffshore use unless installed on a fixed platform. Similarly, the term“inland barge” does not include ocean-going vessels which are mobileunder their own power. Rather, the inland barge is transported via dryhaul lift ship to a location within a commercially practical distancefrom an appropriate natural gas reserve. Commercially practicaldistances are those in which a pipeline from the reserve to the bargemay be constructed while maintaining the total cost of synthetic crudeor hydrocarbon product production within competitive market limits. Suchdistances vary according to the structure of the intervening terrain aswell as other production and market factors, such as then current marketprices for the hydrocarbon products to be produced and local laborcosts.

The GTL barge may be split into numerous sections, for example, anatural gas purification section, a natural gas liquid recovery section;a syngas production section; a Fischer-Tropsch Reaction (“FTR”) section;and a product separation/upgrading section. These sections may or maynot be modules as equipment from one section may be intermingled withequipment from another section. Alternatively, each section may besubstantially self-contained and located substantially separately fromthe other sections.

For the production of syngas, two basic methods have been employed. Thetwo methods are steam reforming, wherein one or more light hydrocarbonssuch as methane are reacted with steam over a catalyst to form carbonmonoxide and hydrogen, and partial oxidation, wherein one or more lighthydrocarbons are combusted or reacted sub-stoichiometrically to producesynthesis gas.

The basic steam reforming reaction of methane is represented by thefollowing formula:CH₄+H₂O+Catalyst→CO+3H₂

The steam reforming reaction is endothermic and a catalyst containingnickel is often utilized. The hydrogen to carbon monoxide ratio of thesynthesis gas produced by steam reforming of methane is approximately3:1.

Partial oxidation is the non-catalytic, sub-stoichiometric combustion oflight hydrocarbons such as methane to produce the synthesis gas. Thebasic reaction is represented as follows:CH₄+½O₂→CO+2H₂

The partial oxidation reaction is typically carried out using highpurity oxygen. High purity oxygen can be quite expensive. The hydrogento carbon monoxide ratio of synthesis gas produced by the partialoxidation of methane is approximately 2:1.

In some situations these approaches may be combined. A combination ofpartial oxidation and steam reforming, known as autothermal reforming,wherein air is used as a source of oxygen for the partial oxidationreaction has also been used for producing synthesis gas heretofore.Autothermal reforming is a combination of partial oxidation and steamreforming where the exothermic heat of the partial oxidation suppliesthe necessary heat for the endothermic steam reforming reaction. Theautothermal reforming process can be carried out in a relativelyinexpensive refractory lined carbon steel vessel whereby low cost istypically involved.

The autothermal process generally results in a lower hydrogen to carbonmonoxide ratio in the synthesis gas than does steam reforming alone.That is, as stated above, the steam reforming reaction with methaneresults in a ratio of about 3:1 while the partial oxidation of methaneresults in a ratio of about 2:1. The optimum, ratio for the hydrocarbonsynthesis reaction carried out at low or medium pressure over a cobaltcatalyst is 2:1. When the feed to the autothermal reforming process is amixture of light hydrocarbons such as a natural gas stream, some form ofadditional control is desired to maintain the ratio of hydrogen tocarbon monoxide in the synthesis gas at the optimum ratio of about 2:1.

In some embodiments the syngas production section of the GTL barge is anAutothermal Reforming unit (“ATR”). The ATR section is any capable ofproducing a synthesis gas to be utilized in the associatedFischer-Tropsch reaction section. As will be understood in the art, ATRmay take different forms but generally is comprised of a vessel having areforming catalyst (e.g. nickel-containing catalyst) therein whichconverts the air/steam/natural gas to a synthesis gas. Syngas useful inproducing a Fischer-Tropsch product may contain hydrogen, carbonmonoxide and nitrogen with H₂:CO ratios from about 0.8:1 to about 3.0:1.Operating conditions and parameters of an autothermal reactor forproducing a syngas useful in the process of the invention are well knownto those skilled in the art. Such operating conditions and parametersinclude but are not limited to those disclosed in U.S. Pat. No.6,155,039, and U.S. Provisional Patent Application Ser. No. 60/497,177.

In some embodiments of the invention, an autothermal reforming processis utilized wherein the ATR is fed natural gas and air-derived oxygen.The term “air-derived oxygen” as used herein refers to oxygen obtainedfrom air by means other than a cryogenic air separation plant. Forexample, air may be passed through a selective membrane through whichoxygen is selectively absorbed and/or passed. Such membranes are knownin the art, for example, in U.S. Pat. No. 6,406,518. Included in suchmembranes are those commonly referred to as mixed conductor ceramicmembranes, oxygen ion transport membranes, and ionic/mixed conductormembranes.

The syngas may be optionally preheated before it is delivered to theFischer-Tropsch reactor. As will be understood in the art, FischerTropsch reactors are well known in the art and basically are comprisedof a vessel containing an appropriate catalyst (e.g. cobalt-containingcatalyst) therein. Fischer-Tropsch catalysts include, for example,cobalt, iron, ruthenium as well as other Group IVA, Group VIII and GroupVIIB transition metals or combinations of such metals, to prepare bothsaturated and unsaturated hydrocarbons. There are several knowncatalysts which are used in converting a synthesis gas depending on theproduct desired; e.g., see U.S. Pat. Nos. 6,169,120 and 6,239,184. TheFischer-Tropsch catalyst may include a support, such as a metal-oxidesupport, including for example, silica, alumina, silica-alumina ortitanium oxides. For example, a cobalt (Co) catalyst on transitionalumina may be used. The Co concentration on the support may be betweenabout 5 wt % and about 40 wt %. Certain catalyst promoters andstabilizers, which are known in the art, may optionally be used.Stabilizers include Group IIA or Group IIIB metals, while the promotersmay include elements from Group IVA, Group VIII or Group VIIB. TheFischer-Tropsch catalyst and reaction conditions may be selected to beoptimal for desired reaction products, such as for hydrocarbons ofcertain chain lengths or number of carbon atoms. Any of the followingreactor configurations may be employed for Fischer-Tropsch synthesis:fixed bed, slurry bed reactor, ebullating bed, fluidizing bed, orcontinuously stirred tank reactor (“CSTR”). The FTR may be operated at apressure from about 100 psia to about 800 psia and a temperature fromabout 300° F. to about 6000 F. The reactor gas hourly space velocity(“GHSV”) may be from about 1000 hr⁻¹ to about 15000 hr⁻. Operatingconditions and parameters of the FTR useful in the process of theinvention are well known to those skilled in the art. Such operatingconditions and parameters include but are not limited to those disclosedin U.S. Pat. No. 6,172,124.

Given the safety issues of dealing with pure oxygen, air based systemshave a significant advantage with a mobile or transportable system. Theuse of air instead of pure oxygen for generating synthesis gas in amobile or transportable process wherein hydrocarbon processing equipmentis necessarily located in relatively close proximity to any air oroxygen-handling equipment significantly raises safety, may be lesscapital-intensive and may reduce the size of the plant and facilities.

The product separation/upgrading section includes equipment forprocessing the syncrude products from the FT section to fuel-gradeproducts, namely diesel and naphtha. The upgrading equipment may beinstalled on the GTL barge or may be located on an adjacent platform,barge or onshore facility. Preferably, products are not stored on thebarge but rather transported to a separate location, such as a floatingstorage offloading unit (FSO) farther out from the shore to—hold theproduct. The FSO may be a reconditioned single hull tanker. Productupgrading equipment may include distillation tower(s) as well ashydroprocessing and hydrocracking reactors.

The utilities section supplies the utilities for all the processes.Utilities supplied may include water, steam, power, and miscellaneousequipment; such as a flare. In a preferred embodiment, the flare is aground flare and may be located on an auxiliary deck or separate fromthe GTL barge, such as on shore or on a separate barge or platform.

1. A transportable synthetic liquid hydrocarbon production facilitycomprising: a liquid hydrocarbon synthesis facility comprising: asynthesis gas generator; and a Fischer-Tropsch reactor for receiving andprocessing a synthesis gas produced by the synthesis gas generator andproducing a predominantly liquid hydrocarbon product. wherein thesynthesis gas generator and Fischer-Tropsch reactor are constructed onan inland barge.
 2. The transportable synthetic liquid hydrocarbonproduction facility of claim 1 further comprising: a ground flare. 3.The transportable synthetic liquid hydrocarbon production facility ofclaim 1 wherein the inland barge comprises two or more decks including alowermost deck and wherein no hydrocarbon processing equipment islocated beneath a lowermost deck.
 4. The transportable synthetic liquidhydrocarbon production facility of claim 2 wherein the ground flare isplaced on an auxiliary deck.
 5. The transportable synthetic liquidhydrocarbon production facility of claim 2 wherein the ground flare islocated on land accessible to the inland barge by piping.
 6. Thetransportable synthetic liquid hydrocarbon production facility of claim1 wherein the hydrocarbon synthesis facility further comprises a productupgrading unit
 7. The transportable synthetic liquid hydrocarbonproduction facility of claim 6 wherein the upgrading unit comprises oneor more units selected from the group of hydrocracking unit,hydrotreating unit, and hydrodewaxing unit.
 8. The transportablesynthetic liquid hydrocarbon production facility of claim 1 furthercomprising a natural gas liquid production unit for extracting propaneand higher carbon number hydrocarbons from a natural gas stream beforethe natural gas is fed into the synthesis gas generator.
 9. Thetransportable synthetic liquid hydrocarbon production facility of claim1 further comprising a natural gas liquid production unit for extractingpropane and higher carbon number hydrocarbons from a tail gas streamfrom a Fischer-Tropsch reactor.
 10. The transportable synthetic liquidhydrocarbon production facility of claim 1 wherein the synthesis gasgenerator is an autothermal reformer.
 11. The transportable syntheticliquid hydrocarbon production facility of claim 1 further comprising anassociated utility section.
 12. The transportable synthetic liquidhydrocarbon production facility of claim 11 wherein utility componentsare located between hydrocarbon vessels and/or process equipment andignition sources.
 13. The transportable synthetic liquid hydrocarbonproduction facility of claim 10 wherein the autothermal reformer is fednatural gas from a stranded natural gas reserve and air oroxygen-enriched air.
 14. A process for producing synthetic liquidhydrocarbons from natural gas at or near calm water comprising the stepsof: dry hauling a mobile synthetic liquid hydrocarbon productionfacility to or near the calm water location; installing the mobilehydrocarbon production facility so that it is not freely floating;connecting the mobile hydrocarbon production facility to a source ofnatural gas; and synthesizing heavier hydrocarbons from the natural gas.15. The process of claim 14 further comprising the step of transferringthe produced heavier hydrocarbon product to an FSO.
 16. The process ofclaim 14 wherein the heavier hydrocarbon product is synthetic crude. 17.The process of claim 14 further comprising the step of upgrading theheavier hydrocarbon product into a transportation fuel.
 18. The processof claim 15 wherein the FSO is a reconditioned single hull tanker. 19.The process of claim 14 wherein the heavier hydrocarbon is predominantlya liquid hydrocarbon.
 20. The process of claim 14 wherein thetransportable liquid hydrocarbon facility is constructed on an inlandbarge.
 21. The process of claim 14 wherein the transportable syntheticliquid hydrocarbon facility is dry hauled by use of a lift ship.
 22. Thetransportable facility of claim 1 wherein air-derived oxygen is fed tothe synthesis gas generator.
 23. The process of claim 14 wherein thecalm water location has wave action of no greater than that of Sea State0.